A collision between a British nuclear-powered submarine carrying multiple nuclear warheads and a French nuclear submarine armed with a similar payload may have been the result of lack of communication between France and NATO nations, according to a former British submarine commander whose revelations were partially corroborated by an official at the French navy.

Sometime on Feb. 3 or 4, the British HMS Vanguard and France's Le Triomphant collided in the midAtlantic Ocean. The accident probably happened because the two submarines were not aware of each other. NATO operates a traffic-control system that alerts allied nations to the deployment zones of friendly submarines. The system is designed to avoid collisions. But because France is not part of NATO's military command structure, it does not provide information on the location of its mobile nuclear arms to that system, according to Julian Ferguson, who commanded one of Britain's four V-class nuclear submarines before retiring in 2006. (See a graphic of the global nuclear arms balance.)

"There is a system for operating areas that are reserved for American, British, Norwegian, Dutch and Canadian communities, and if you want to go into someone's area of influence, you tell them what you are doing. But if you are not in the NATO military structure, you don't have to do that," says Ferguson.

The French navy confirmed to TIME that it does not give the positions of its nuclear-armed submarines to NATO forces. "France does not supply any information regarding the position of its nuclear arms or submarines carrying them because France considers its nuclear arsenal the most vital element in its defense capabilities," said Jérome Erulin, a spokesman for the French Navy.

NATO sources told TIME that France is not alone in withholding information about nuclear-armed submarines  the Brits and Americans keep the locations of their strategic deterrents secret too. In a prepared statement, a NATO spokesman said, "France uses the same procedures with regard to its submarine fleet as all other allies."

But Ferguson says the French are particularly secretive due to their position outside NATO's command structure. And past policy-level discussions have suggested a concern over the lack of communication. In 1994 Britain and France discussed closer cooperation between their navies and a possible carving up of deployment zones for their nuclear-armed submarine patrols. It took until September 2000 for arrangements to be formalized, in what was named the U.K.-French Bilateral Defense Cooperation Agreement. That called for port visits for British and French nuclear-armed submarines and regular exchanges on nuclear policy. (See pictures of the French President visiting the U.K.)

But it's unclear whether the agreement called for an exchange of information regarding nuclear-armed submarine positioning; many arms experts say it probably did not. "The fact that the collision occurred at all indicates that the two allies need to talk more," says Hans Kristensen, who monitors NATO's weapons for the Federation of American Scientists.

While the intersection of two sonar-equipped nuclear submarines in a vast ocean may seem an unlikely event even without communication, there are environmental anomalies in the Atlantic that make a collision more likely, according to Ferguson. Submarines on a deterrent mission, for instance, tend to congregate in places where they are unlikely to be found by other submarines and spy planes. "There are oceanographic factors in which you can be on either side of an ocean front where the temperature is slightly different on your side than the others," says Ferguson. "Where the gulf stream comes across the Atlantic is a prime point of this. Sometimes these barriers can be quite hard  no sound penetrates at all. And if your business is hiding, then you would hide in that vicinity. There is an added risk that, given the environmental factors, maybe you don't hear another submarine in time to do something about it."

The multiple city-destroying warheads on the French and British submarines are not at risk of detonation from collision, Ferguson says. But had a nuclear reactor been damaged on either boat, it could have poisoned the crew and spread radioactive waste for miles across the Atlantic.

If in fact the collision could have been prevented by better communication between France and NATO, the revelation comes at a politically sensitive time: France is set to rejoin NATO's military infrastructure in April. Its secrecy policy on the location of its nuclear-armed subs could come under fire before then, especially as the French say they will not budge on the issue. Explains Erulin of the French Navy: "Because this is so essential to France's strategic defense interests, this is something that will be maintained even after France is fully reintegrated into NATO's military command structure."